Pickup trucks are motor vehicles with a rear open-top cargo area that is often referred to as a cargo box. The cargo box has a bed, opposing sidewalls, a header, and a tailgate. The box is attached to and supported by the chassis. The opposing sidewalls include inner and outer panels connected together along the top rail and at other selected locations to allow relative movement between the inner and outer panels. This leaves the large portions of outer panel unsupported, and the outer panel is self-supporting and relies on its own strength to resist panel deflections (such as oil canning), waviness, and other deformations. (Oil canning is when the panel elastically deflects inwardly in response to a force.) Traditional outer panels are formed from steel, which is able to resist panel deflections without the need for additional support structures within the sidewalls.
Pickup-truck boxes are being formed of aluminum alloys to improve vehicle performance and fuel economy. Aluminum alloy may have a higher strength-to-weight ratio than steel, and replacing steel with aluminum alloy offers the potential for weight reduction. The elastic modulus of aluminum is generally lower than the elastic modulus of steel. Thus, many fabrication techniques and joining methods that work well for steel parts do not work well for the same aluminum part. Due to these and other differences, simple material substitution does not necessarily produce an acceptable design.
Aluminum panels are more susceptible to oil canning than steel panels. Commercially viable aluminum panels must be resistant to oil canning and other panel deformation. This disclosure is directed to solving these and other problems associated with aluminum outer panels as will be described in more detail below.